High frequency attenuator means



' Aug. 21, 1956 5 MAY HIGH FREQUENCY ATTENUATOR MEANS Filed Dec. 16. 1952 FIG.

ml 7 l 7 I a w. M ml &\ n l4 6 Z I an 7 v I Urn INVENTOR A. 5". MA Y BY ATTORNEY United States Patent HIGH FREQUENCY ATTENUATOR NIEANS Allan S. May, Chatham, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 16, 1952, Serial No. 326,237

2 Claims. (Cl. 33381) This invention relates to attenuators and more particularly to attenuators suitable for use at relatively high frequencies.

In order to provide suitable attenuation in high frequency circuits comprising Wave guides, coaxial conductors and the like, it is often necessary to construct attenuating devices with extreme accuracy at relatively high cost, particularly where the impedance requirements are quite rigid. In many cases, relatively rigid but somewhat less stringent requirements could be met if suitable means for adapting ordinary types of resistors to high frequency use were available. This invention deals with such an adaptation.

An object of this invention is to reduce the cost and simplify the construction of high frequency attenuators.

One feature of this invention resides in a fixture or housing suitable for connection into a coaxial line and containing a plurality of resistors connected for insertion in the line.

Another feature of this invention lies in the physical arrangement of the resistors with respect to each other to avoid undesirable capacity effects.

A further feature involves the correlation of the housing with respect to the resistors in order to minimize unwanted impedance elfects.

Other and further objects and features of this invention will appear more fully and clearly from the following description of an illustrative embodiment thereof taken in connection with the appended drawings in which:

Fig. l is :a plan view of a device embodying this invention, with the cover removed to show internal structure; and

Fig. 2 is a perspective view of the embodiment of Fig. 1 with the cover separated from the fixture.

This attenuator comprises a housing generally indicated by the numeral and formed of two like parts consisting of a body portion 11 and a cover portion 12. The body and cover are of substantially the same size and configuration. Each portion of the housing is provided with a channel or duct 13 having an enlarged cylindrical intermediate portion or cavity 14.

Coaxial jacks or connectors 15 are attached to either end of the housing 10 by end plates or flanges 16. The end plates are held in place on the housing by suitable means such as the screws 17. The two parts 11 and 12 of the housing are held together by screws (not shown) passing through the openings 18 in the cover 12 into tapped holes 19 in the body 11. The end plates 16 besides supporting the jacks 15 provide covers for the ends of the channel 13.

Mounted in the enlarged portion or cavity 14 of the channel 13 are resistors 21, 22 and 23 arranged in parallel coplanar relation. These resistors may be of the pigtail type having leads projecting from either end. The

resistor 22 is connected between the inner conductors of the coaxial jacks, thus comprising a series resistor. The resistor 21 is connected at one end to the resistor 22 and at the other end to the body portion 11 of the housing by means of a connector or binding post 24. The resistor 23 is similarly connected to the other end of the resister 22 and to another connector 24 on the body portion 11. The resistors 21 and 23 serve as parallel arms of a 11' type network, the series resistor of which is 22.

It will be noted that the parallel resistors 21 and 23 are relatively widely separated thereby reducing the capacity effect between them. Such a minimizing of this capacity is advantageous since it would shunt the series resistor.

The walls of the channel 13 and its enlargement 14 are proportioned so that the capacitative reactance of the housing walls substantially balances the inductive reactance of the resistor elements and their connecting leads in the frequency range of interest. The particular device shown was designed particularly for a frequency range of from 60 to megacycles. Suitable dimensions for this range are for the channel, length 1.375 inches, width 0.5625 inch, depth 0.3125 inch and for the enlargement or cavity 0.875 inch diameter. By using such proportions the impedance effect of the device is rendered essentially resistive for the frequency range of interest.

What is claimed is:

1. An attenuator comprising a housing, two aligned coaxial line sections extending oppositely from said housing, the walls of said housing defining a duct in alignment with the line sections, said duct having an enlarged cylindrical intermediate portion, and three elongated resistors disposed in said intermediate portion and lying in the same plane, one of said resistors being in line with and connected between the inner conductors of said coaxial line sections, the other two resistors lying respectively on opposite sides of said one resistor and parallel thereto, said other resistors being connected respectively between opposite ends of said one resistor and said housing to form therewith a 1r type network, the spacing between the housing walls, and the resistors and their connections being such that the inductive and the capacitative reactances of the :assembly are substantially balanced for the frequency range of interest.

2. An attenuator comprising a conductive housing, two aligned coaxial line sections extending oppositely from said housing, the walls of said housing defining a duct in alignment with the line sections, said duct having an enlarged intermediate portion, and three resistors disposed in said intermediate portion, one of said resistors being in line with and connected between the inner conductors of said coaxial line sections, the other two resistors lying respectively on opposite sides of said one resistor and parallel thereto, said other resistors being connected respectively between opposite ends of said one resistor and said housing, the spacing between the housing walls and the resistors and their connections being such that the inductive and the capacitative reactances of the assembly are substantially balanced for the frequency range of interest.

References Cited in the file of this patent UNITED STATES PATENTS 2,429,401 Davis Oct. 21, 1947 2,619,540 Lundstrom Nov. 25, 1952 FOREIGN PATENTS 628,737 Great Britain Sept.. 5, 1949 

